Lee W. Kohlman, Charles R. Ruggeri, Gary D. Roberts, and Robert F. Handschuh

Glenn Research Center, Cleveland, Ohio

Improvements in High Speed, High Resolution

Dynamic Digital Image Correlation for

Experimental Evaluation of Composite 

Drive System Components

NASA/TM—2013-216537

July 2013
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Lee W. Kohlman, Charles R. Ruggeri, Gary D. Roberts, and Robert F. Handschuh

Glenn Research Center, Cleveland, Ohio

Improvements in High Speed, High Resolution

Dynamic Digital Image Correlation for

Experimental Evaluation of Composite 

Drive System Components

NASA/TM—2013-216537

July 2013

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

69th Annual Forum and Technology Display (AHS Forum 69)

sponsored by the American Helicopter Society

Phoenix, Arizona, May 21–23, 2013
Acknowledgments

Funding for this work has been provided by NASA’s Rotary Wing Project. Assistance with the accelerometer data collection was 

provided by Kelsen LaBerge and Paula Dempsey at NASA Glenn Research Center. Ongoing analysis of the accelerometer data 

is being performed by Han DeSmidt of the University of Tennessee.

Available from

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Trade names and trademarks are used in this report for identifi cation 

only. Their usage does not constitute an offi cial endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

This work was sponsored by the Fundamental Aeronautics Program 

at the NASA Glenn Research Center.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2013-216537 1 

Improvements in High Speed, High Resolution Dynamic 

Digital Image Correlation for Experimental Evaluation 

of Composite Drive System Components 

Lee W. Kohlman, Charles R. Ruggeri, Gary D. Roberts, and Robert F. Handschuh 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

Composite materials have the potential to reduce the weight 

of rotating drive system components. However, these 

components are more complex to design and evaluate than 

static structural components in part because of limited ability 

to acquire deformation and failure initiation data during 

dynamic tests. Digital image correlation (DIC) methods have 

been developed to provide precise measurements of 

deformation and failure initiation for material test coupons and 

for structures under quasi-static loading. Attempts to use the 

same methods for rotating components (presented at the AHS 

International 68th Annual Forum in 2012) are limited by high 

speed camera resolution, image blur, and heating of the 

structure by high intensity lighting. Several improvements 

have been made to the system resulting in higher spatial 

resolution, decreased image noise, and elimination of heating 

effects. These improvements include the use of a high 

intensity synchronous microsecond pulsed LED lighting 

system, different lenses, and changes in camera configuration. 

With these improvements, deformation measurements can be 

made during rotating component tests with resolution 

comparable to that which can be achieved in static tests. 

Introduction 

A new high speed DIC measurement technique was used to 

measure the deformation near a damaged site for a composite 

tube rotating at 5000 rpm at torques up to 1130 Nm 

(10,000 in.-lb) and to examine the deformation of a diaphragm 

element of a flexible composite coupling also rotating at 

5000 rpm at torques up to 1130 Nm (10,000 in.-lb). These 

results will be presented along with results of an initial attempt 

to detect damage in the rotating composite tube by processing 

of accelerometer data taken at the bearing mounts. 

Previous testing presented by Kohlman (Ref. 1) showed that 

digital image correlation on high speed rotating components is 

primarily limited by lighting and exposure times. Tests 

performed using metal halide based continuous lighting was 

not sufficient to provide enough light without causing 

excessive heating of the test article and was not suitable to 

sustained operation. The result was longer camera shutter 

times which causes more image blur and higher noise levels. 

To get to the required illumination levels without excessive 

heating, an image synchronous pulsed LED illumination 

source was used. The LED based system is capable of very 

short pulse durations with fast rise and fall times and high 

repetition rates. Commercially available drivers capable of 

2 sec pulses were used, though shorter pulse drivers could be 

constructed for shorter exposure. The result was DIC results 

with noise levels comparable to stationary imaging. 

These improvements will allow for more precise data to be 

collected on composite rotating structure with sufficient 

resolution to identify local damage and failure processes 

during operation. Rotation and torque tests were performed 

using a composite tube with varying levels of damage and 

with a composite flexible element. These tests were performed 

in the High Speed Helical Gear Test rig at NASA Glenn 

Research Center. More information on the test rig is provided 

by Handschuh (Refs. 2 to 4). Acceleration data was also 

collected at the bearing mounts to determine if the damage 

could be detected remotely. 

A high resolution camera system is also being developed 

that uses a pair of 29 megapixel cameras and pulsed LED 

lighting to acquire higher resolution images and further 

improve the capability for damage detection in rotating 

composite structures. 

Synchronous Pulsed Led Lighting 

LED lighting can be used to produce extremely intense 

pulses of light with high repetition, fast rise and fall times, and 

short duration (Refs. 5 and 6). Most LEDs available today are 

typically limited to only a few watts. To achieve the high level 

of illumination required, many individual LEDs are needed. 

Because the LEDs are operated in a pulsed mode with a very 

low duty cycle, heat dissipation of the array is not a significant 

concern, however the individual LED experiences rapid 

heating and cooling and severe electrical stresses. 

First Generation LED Array 

A compact LED array, shown in Figure 1, was constructed 

to provide the high illumination required for the short duration 

exposures required by the high speed imaging. The array is 

composed of 90 Cree XM-L 4500 k white LEDs rated at 

1.5 A maximum continuous current. The LEDs were 

individually fitted with 12 degree optics (typically specified 

for Cree XP-G LEDs) and a 45.7 cm (18 in.) focal length 
NASA/TM—2013-216537 2 

Figure 1.—High intensity pulsed LED light array. 

Fresnel lens was used to focus the light into an area roughly 

15.2 cm (6 in.) square. The LEDs are connected in series 

(9 LEDs per string) with 5 strings wired in parallel. Each set 

of 5 strings were connected to one channel of an Advanced 

Illumination Pulsar 320 LED driver that supplies 2 channels at 

50 A per channel or 10 A per string (6.7 times the continuous 

rated LED current). The LEDs were operated with pulse 

duration of 2 sec with an effective driving power of 

approximately 3000 W. Heating of the composite test article 

due to the lighting, as was previously experienced using 

1200 W of metal halide lighting, was not a limitation because 

the short pulse duration and relatively low repetition rate 

(1000 Hz) results in an average power of less than 6 W. Six 

additional LEDs are operated continuously to enable 

positioning of the array. The pulsed illumination appears very 

dim to the human eye because of the low duty cycle. 

An image of the cameras, LED array (copper plate in front 

of the cameras), and composite tube installed in the test rig is 

shown in Figure 2. The high speed cameras are Phantom V10 

cameras with a 4 megapixel black and white sensor. The 

triggering method is similar to the previously reported system 

(Ref. 1) except for the addition of the LED system and a 

variable timing delay between camera and LED trigger signals 

provided by the microcontroller. Before synchronous 

operation, the camera and LED triggers are operated at a user 

specified frequency to avoid timeout. A button on the 

microcontroller switches the microcontroller over to 

synchronous operation at the beginning of the test. An optical 

sensor is used to provide a pulse as reflective strips on the 

shaft pass by. One or multiple reflective strips can be used. 

The microcontroller counts the pulses from the optical sensor 

and triggers the cameras at the desired locations and rotation 

intervals. In this way, one location or the entire shaft can be 

imaged at any rotation interval. The separate trigger signals 

provided by the microcontroller allow for sub-microsecond 

compensation of the trigger latency difference between the 

cameras and LED driver. 

Second Generation LED Array 

After the first LED array was successfully tested, a second 

more compact array was designed. The new array will be 

10.2 cm (4 in.) square and made from aluminum instead of 

copper. A rendering is shown in Figure 3. This array differs in 

Figure 2.—Image of the cameras (right), LED array (middle), 

and shaft (left). 

Figure 3.—Rendering of the second generation LED array. 

several important ways from the first version. This array uses 

14 LEDs wired in series to take better advantage of the 

driver’s voltage capability. Two arrays will be wired in 

parallel to each channel of the driver so that up to 25 A (more 

than 16 times the rated continuous current) will be delivered to 

each LED instead of the previous 10 A. Also, each LED is 

mounted to a separate surface on the mounting plate that is 

angled such that all LEDs converge at a distance of 45.7 cm 

(18 in.). By angling each LED, the secondary Fresnel lens was 

eliminated, resulting in less scattering and absorption. The 

arrays will also be lighter and smaller making setup easier and 

allowing for lighting from multiple angles. Four panels will be 

driven by a single driver and supply almost 50 percent more 

light than the original array with 34 fewer LEDs. 

Rotating Composite Structure 

Failure of composite structure, particularly those with large 

fiber architecture, can often be attributed to initiation at local 

defects or damage sites. For example, the onset of a torsional 

buckling instability or material failure of a tube could be 

initiated by a local non-uniform deformation region near a 

defect or damage site in the tube. In previous quasi-static 

testing of flat coupons and tubes, localized high strain 

deformation and the onset of localized damage (e.g., splitting 

within fiber bundles and delamination between fiber tows) 

could be detected using full field DIC with appropriate camera 

resolution, lenses, and field of view. (Refs. 7 to 9). As 
NASA/TM—2013-216537 3 

mentioned earlier in this paper, it is not currently possible to 

get the same spatial resolution in DIC measurements on 

rotating structures. This paper describes advancements that 

have been made to enable detection of local material 

deformation near a damage site in a rotating tube. Also 

described are further advancements that are in progress to 

enable measurement of damage such as splitting of fiber 

bundles and inter-tow delamination in a rotating structure at 

resolutions comparable to that achievable in current static tests. 

Rotating Composite Tube Test 

Preliminary testing of the high speed DIC method on a 

rotating composite tube was reported by Kohlman (Ref. 1) in 

2012. A second shaft was constructed using the previously 

reported methods. The same quasi-isotropic triaxial braid 

construction was used. 

Evaluation of the new pulsed LED system was performed 

on the new composite tube with 3 levels of damage 

(undamaged, an offset 6.35 mm (1/4 in.) diameter thru-drilled 

hole, and an “X” notch cut through the 6.35 mm (1/4 in.) hole 

with a cut off wheel). The “X” notch damaged tube is shown 

installed in Figure 4. Tests were performed at various speeds 

and torques to determine DIC noise levels and minimum strain 

and displacement resolution and for collection of 

accelerometer data. The accelerometers are visible on the 

bearing mounts at the ends of the blue wires in Figure 4. 

Analysis of the accelerometer data is ongoing. 

Data were collected under the following conditions for the 

composite tube in all three damage states: 

1. Speed ramp to 5000 rpm immediately followed by a 

torque ramp to 1130 Nm (10,000 in.-lb) or roughly 

560 kW (750 hp) 

2. Speed step increase (1000, 2000, 3000, 4000, and 

5000 rpm) with a 113 Nm (1000 in.-lb) torque applied to 

prevent chatter 

3. Torque step increases at 113, 282, 565, 847, and 1130 Nm 

(1000, 2500, 5000, 7500, and 10,000 in.-lb) at 5000 rpm 

4. Speed step decrease (5000, 4000, 3000 rpm) at full torque 

(1130 Nm or 10,000 in.-lb) 

Figure 5 (top) is a plot of the standard deviation of major 

strain at different operating speeds with 113 Nm (1000 in.-lb) 

torque. The values of major strain were taken from the 

location shown in the major strain map (Fig. 5, bottom). Ten 

stages were used at each operating speed to calculate the 

standard deviation. There is little dependence of standard 

deviation on operating speed and all values are very low, less 

than 0.03 percent at this location. Variation is expected to 

increase near the edges of the measurement region because of 

a greater out-of-plane component and the images become outof-focus. This also results in the elliptic measurement region 

visible in the major strain map on the bottom in Figure 5. 

Previous testing using metal halide lighting showed a 

significant increase in variation with speed and required the 

Figure 4.—Composite tube in machine with the most severe 

damage “X” notch. 

Figure 5.—Plot of the standard deviation of major strain at 

different rotational speeds (top) and an example major 

strain map showing the point used for the standard 

deviation measurement (bottom). 

limit on a parameter in the DIC software known as 

intersection deviation to be raised to 1.5 pixels to successfully 

process the DIC project. Data acquired with the new system 

was successfully processed at the default value of 0.3 pixels. 

The data in Figure 5 were collected on the damaged composite 

tube with the 6.35 mm (1/4 in.) diameter hole, visible in the 

image on the bottom. 

Figure 6 is an example of the resolved radial displacement 

(top) and shear strain (bottom) observed near the “X” notch in 

the composite tube. Due to the relatively thick tube wall and 

torque limited to 1130 Nm (10,000 in.-lb), very little 

deformation was observed in the undamaged test. Previous 
NASA/TM—2013-216537 4 

Figure 6.—An example of torque induced radial displacement (top) and shear strain (bottom) around the “X” 

notch in the composite tube at 5000 rpm and 1130 Nm 

(10,000 in.-lb). 

tests on an impact damaged composite tube showed similar 

patterns but were very difficult to identify except at the 

highest loading. The failure torque of the undamaged 

composite tube is expected to exceed 9040 Nm (80,000 in.-lb). 

The tube was not tested to failure in a static test, however a 

similar tube with a known mold line defect was tested and 

failed at 6200 Nm (55,000 in.-lb) with failure initiating at the 

defect site. 

Composite Flexible Element 

Flexible shaft couplings add a significant amount of weight 

to rotorcraft drive systems. One possible concept to reduce the 

weight of these components is to construct a flexible element 

which is integral to the shaft. This eliminates the need for 

additional fasteners and flanges, however the durability and 

fatigue characteristics of such a structure is an area warranting 

more detailed investigation. High speed DIC on these 

structures could provide data needed for model development 

and assist with damage detection and deformation mode 

Figure 7.—Filament wound flexible composite element 

mounted in the test rig. 

Figure 8.—Close-up DIC at 5000 rpm on a filament wound 

composite flex element showing local radius measurement 

(top), and resolved local surface texture (bottom). 

characterization during operation. In order to evaluate the high 

speed DIC methods on a coupling with complex shape, 

filament wound flexible elements were acquired from Lawrie 

Technology, Inc. These flexible elements have a more 

complex geometry and smaller tow size than the previously 

tested composite tubes. Tests that were performed included 

some of the various speed and torque conditions used in the 

damaged tube tests. The mounted test article is shown in 

Figure 7. 

Figure 8 shows examples of the resolved features in a small 

section near one end of the test element. Again, the improved 

lighting reduces measurement noise and allows for the use of a 

smaller field of view on the test article while operating at 

5000 rpm. 100 mm lenses were used for this test and the 

cameras were mounted such that the intersection of the focal 

planes was parallel to the rotation axis (the camera assembly 

was tilted 90 compared to what is shown in Fig. 2). 

At the load limit of 1130 Nm (10,000 in.-lb), very little 

deformation was observed. 
NASA/TM—2013-216537 5 

High Resolution DIC 

Higher resolution images allow for more detailed 

investigation of composite damage and failure under load 

(Refs. 7 to 9). A custom camera system is being built to 

acquire images for DIC using a pair of 29 megapixel machine 

vision cameras. The GX6600 camera from Allied Vision was 

selected for this system. This camera uses the Kodak 

Truesense KAI-29050 sensor with a resolution of 6576 by 

4384 pixels. 

This camera is capable of a minimum shutter of 30 sec but, 

with the pulsed illumination method, it may be possible to 

achieve effective shutter times of 2 sec with the current LED 

drivers. Figure 9 is a sketch of the new camera system 

operational layout. A position sensor provides a signal to the 

Camera and LED Controller which then triggers the LED 

drivers and Cameras. Images from the Cameras are then saved 

to the Acquisition Computer using dual gigabit Ethernet 

(GigE) lines with Link Aggregation from each camera. The 

Acquisition Computer uses a quad GigE PCI Express card and 

a striped RAID 0 hard drive array to maintain the maximum 

data transfer rates. The Camera and LED Controller consists 

of a mini-ITX computer case with a Raspberry Pi 

microcontroller and interfacing circuit installed within. Power 

for the cameras and Raspberry Pi is supplied by the built-in 

ATX power supply. The Raspberry Pi operates with a Debian 

Linux operating system and can be controlled wirelessly (USB 

WIFI dongle) via a Secure Shell (SSH). The Acquisition 

Computer operates with an Ubuntu Linux operating system 

and can also be interfaced using SSH. Images can be 

transferred from the Acquisition Computer to another 

computer using FTP or any other desired file transfer protocol 

using the onboard (5th) GigE adapter. 

Figure 9.—Mode of operation schematic. 

A simple 2D demonstration was performed with the 

29 megapixel cameras to show that the larger images can be 

used with existing DIC software and to document the possible 

increase in data resolution. The demonstration used a single 

camera and a 100 mm lens with a working distance of roughly 

45.7 cm (18 in.). The camera was then calibrated using the 2D 

DIC procedure. The field of view was roughly 8 by 10 cm 

(3.1 by 3.9 in.). Figure 10 (top) shows a previously tested 

braided composite coupon with the same architecture as the 

composite tube discussed earlier. A stochastic pattern was 

applied using a fine spray paint mist. The scale bar is 

approximate. The combination of increased resolution and 

narrow optics resulted in spatial resolution greater than 

55 pixels/mm (1400 pixels/inch). The DIC facet and step size 

were set to 11 and 7 pixels, respectively. This generated a data 

resolution of 8 data points/mm (200 data point/inch). The 

bottom of Figure 10 shows a close up of the image with the 

data point grid (7 pixel spacing) overlaid. A single tow 

3.5 mm (0.14 in.) wide is visible. The 29 megapixel DIC is 

capable of resolving much smaller features while increasing 

the overall field of view. 

Figure 10.—29 megapixel image (top) and data point 

grid (bottom). 
NASA/TM—2013-216537 6 

Conclusions 

The high intensity synchronous pulsed LED illumination 

method was successful in reducing the noise during image 

capture on rotating composite components for digital image 

correlation measurement. The effects of blur were minimized 

and noise levels comparable to static operation were observed. 

Also, heating of the component was eliminated by replacing 

the high intensity metal halide lights used previously with 

more intense, but low duty cycle LED illumination. 

Development of the high resolution DIC system is underway 

and preliminary tests indicate that no difficulties with the 

commercially available DIC software are expected when 

processing the larger images. The achievable field of view and 

spatial resolution will allow more detailed investigation of the 

local damage and failure mechanisms of the composite 

architecture. Synchronous pulsed illumination is expected to 

produce effective shutter times of 2 sec with the 

29 megapixel cameras (minimum shutter time of 30 sec), but 

this has not yet been tested. A higher torsion load limit is 

required to produce damage and/or failure in the components 

tested to better demonstrate the capability of detecting local 

damage during rotational operation. 

References 

1. Kohlman, L.W., Ruggeri, C.R., Martin, R.E., Roberts, 

G.D., Handschuh, R.F., and Roth, D.J., “Full-field 

Deformation Measurement Techniques for a Rotating 

Composite Shaft,” American Helicopter Society 68th

Annual Forum Proceedings, Fort Worth, TX, May 2012. 

2. Handschuh, R. and Kilmain, C., “Experimental Study of 

the Influence of Speed and Load on Thermal Behavior of 

High-Speed Helical Gear Trains,” NASA TM-2005-

213632, July 2005. 

3. Handschuh, R. and Kilmain, C., “Operational Influence 

on Thermal Behavior of High-Speed Helical Gear 

Trains,” NASA TM-2006-214344, November, 2006. 

4. Handschuh, R., Kilmain, C., and Ehinger, R., 

“Operational Condition and Superfinishing Effect on 

High-Speed Helical Gearing System Performance,” 

NASA TM-214696, June 2007. 

5. Aikio, M., Lindström, H., Juntunen, E., Kataja, K., and 

Keränen, H., “Pulsed LED Illumination for High Speed 

Imaging,” Key Engineering Materials, Vols. 364-366, 

2008, pp. 827-831. 

doi:10.4028/www.scientific.net/KEM.364-366.827 

6. Willert, C., Stasicki, B., Klinner, J., and Moessner, S. 

“Pulsed Operation of High-Power Light Emitting Diodes 

for Imaging Flow Velocimetry,” Measurement Science 

and Technology, Vol. 21, June 2010, pp. 1-11. 

doi:10.1088/0957-0233/21/7/075402 

7. Kohlman, L.W., “Evaluation of Test Methods for Triaxial 

Braid Composites and the Development of a Large 

Multiaxial Test Frame for Validation Using Braided Tube 

Specimens,” Ph.D. Dissertation, The University of Akron, 

Akron, Ohio, 2012. 

8. Kohlman, L.W., Bail, J.L., Roberts, G.D., Salem, J.A., 

Martin, R.E., and Binienda, W.K., “A notched coupon 

approach for tensile testing of braided composites,” 

Composites: Part A, Vol. 43, Issue 10, October 2012, pp. 

1680-1688. doi: 10.1016/j.compositesa.2011.12.013 

9. Littell, J.D., “The Experimental and Analytical 

Characterization of the Macromechanical Response of 

Triaxial Braided Composite,” Ph.D. Dissertation, The 

University of Akron, Akron, Ohio, 2008.